Mermane was a female humanoid demon, she had purple skin with a pair of large eyes on her shoulders, she had a pair of shells under her breasts. She had a pair of gills on her waist and several short tentacles around her waist and a octopus like head on her crotch, across her breasts is a large toothed mouth. she had fins down the lower half of her arms. She had scaled legs and webbed feet, she had a large crest on her forehead with a pair of small glowing eyes on it, her ears were a pair of small down pointing fins and she had a large shark fin on the top of her head with massive fins on either side.

Little of the sea demoness back story is known however at one point presumably during the apocalypse set off by Lacock she fused with the female and recently widowed school teacer Jun, however instead of taking over, Jun remained dominant and became a Devilman.